The present disclosure relates generally to cardiac rhythm management systems and, more particularly, to a cardiac imaging system and method for quantification of desynchrony of ventricles for biventricular pacing.
It is estimated that approximately 6-7 million people in the United States and Europe alone have congestive heart failure (CHF), with ischemic and idiopathic cardiomyopathies being the most common causes of CHF. In about 20-50% of patients having CHF, the associated electrocardiograms are characterized by prolonged PR intervals and wide QRS complexes. Moreover, about 29% of these patients have left bundle branch block (LBBB).
In a normal heartbeat, the electrical conduction begins in the sinoatrial (SA) node (a small group of muscle cells in the upper right part of the upper right heart chamber, i.e., the right atrium). Impulses sent out by the SA node spread quickly throughout the upper heart chamber and across the atrioventricular (AV) node. Once past the AV node, the electrical signals travel through a bunch of fibers called the bundle of His, which passes the signals the rest of the way through the wall separating the upper and lower heart chambers, splitting down the right and left bundle branches to reach each part of the ventricles.
However, in those patients with CHF and LBBB, a long mechanical delay in the left side of the heart leads to a delayed left ventricular ejection due to delayed left ventricular depolarization. In other words, LBBB causes an asymmetrical contraction of the right and left ventricles. In addition, this condition (also known as desynchrony) may also result in different regions of the left ventricle not contracting in a coordinated fashion. This irregular motion is characterized by shortening of the septum, followed by stretching of the lateral wall. Subsequently, the lateral wall then shortens and the septum stretches, thereby causing an ineffective contraction of the left ventricle.
Cardiac resynchronization therapy, also known as biventricular pacing, is an interventional procedure in which both the right ventricle and left ventricle of the heart are paced simultaneously to improve heart pumping efficiency. In one example of a conventional biventricular pacing procedure, both the right ventricle and right atrial leads are first positioned. Then, a sheath is positioned within the coronary sinus (CS) and a CS angiogram is performed in order to delineate a suitable branch for left ventricle lead placement. After a suitable branch is identified, the left ventricle lead is placed in the posterior or posterolateral branch of the CS. Once positioned, the right and left ventricle leads are paced simultaneously, thus achieving synchronization with atrial contraction.
For many patients, cannulating the CS is the one-step procedure of choice for biventricular lead placement. However, in over 20% of these patients, lead placement in the CS may be unsuccessful or a very lengthy procedure, or the lead may become dislodged from the CS. Other difficulties with this lead placement procedure may also include unavailability of a suitable CS branch, significant rotation of the CS due to left atrium and left ventricle dilation, and the presence of the Thesbesian valve therein. In most instances, these problems are identified only at the time of the interventional procedure, and thus the procedure is typically either completely abandoned or the patient is brought back into the operating room for a second procedure where, through a surgical incision (an expensive and invasive procedure) the left ventricle lead is placed epicardially.
Unfortunately, epicardial lead placement is not without its own pitfalls, some of which include: a limited view of the posterolateral area of the left ventricle using minithoracotomy; the limitation of placement sites providing reasonable pacing and sensing parameters; the inability to determine the distance of the left ventricle from the thoracic wall; the inability to identify the posterolateral or other areas of the left ventricle that contracts last; the potential risk of damaging the coronary arteries and veins; the increased level of difficulty due to the presence of extrapericardial fat; the lack of visualization of normal versus scarred tissue; and the difficulty in identifying the ideal pacing position as a result of one or more of the above.
Accordingly, there is a need for an improved system and method for quantifying the desynchrony of the right and left ventricles so as to provide information for planning biventricular pacing interventional procedures.